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J Immunother. 2015 Apr;38(3):116-26. doi: 10.1097/CJI.0000000000000073.

Proapoptotic and antiapoptotic proteins of the Bcl-2 family regulate sensitivity of pancreatic cancer cells toward gemcitabine and T-cell-mediated cytotoxicity.

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*Section of Gastroenterology, Medizinische Klinik und Poliklinik IV, University of Munich ¶Division of Clinical Pharmacology, Center of Integrated Protein Science Munich (CIPS-M), Medizinische Klinik und Poliklinik IV, University of Munich ‡Institute of Molecular Immunology (IMI), Helmholtz Zentrum München §Immunotherapy Research Center, Immunis e.V., Munich †Institute of Pathology at Medizin Campus Bodensee, Friedrichshafen ∥Division of Molecular Oncology, Institute for Experimental Cancer Research, University of Kiel, Kiel #Kliniken St. Elisabeth, Department of Medicine II, Neuburg an der Donau, Germany.


Sensitivity of carcinoma cells towards gemcitabine (Gem) has been linked to mitochondrial apoptotic proteins. Recently, we described synergistic efficacy of Gem-based chemoimmunotherapy and a dendritic cell (DC) tumor vaccine in a murine pancreatic carcinoma model. Here, we investigated the role of the mitochondrial proteins Bcl-2, Bcl-xL, and Bax for sensitization of pancreatic carcinoma cells toward T-cell-mediated cytotoxicity alone and in combination with Gem. Bcl-2 expression was silenced by siRNA in Panc02 pancreatic cancer cells expressing the model antigen ovalbumin (PancOVA). Tumor cells were treated with Gem and/or siRNA, and cytotoxicity induced by OVA-specific cytotoxic T lymphocytes (CTL) from OT-1 mice was assessed. Gem-induced and T-cell-induced cytotoxicity was also studied in human Colo357 pancreatic cancer cell lines overexpressing Bax or Bcl-xL. Apoptosis induction by Fas-activating antibody was measured by Annexin V staining. The in vivo capacity of Bcl-2 siRNA to augment CTL efficacy induced by DC vaccinations was assessed in C57BL/6 mice bearing PancOVA tumors. PancOVA cells treated with Bcl-2 siRNA were sensitized towards both Gem and T-cell-mediated killing; combination therapy exhibited an additive effect. Bax overexpression sensitized Colo357 cells to both Gem-mediated and T-cell-mediated cytotoxicity, whereas Bcl-xL overexpression was inhibitory. Combining Bcl-2 silencing with DC therapy improved tumor control in the PancOVA model in vivo without affecting the number of tumor-reactive CTL. In conclusion, expression of Bcl-2, Bcl-xL, and Bax in pancreatic tumor cells determines sensitivity towards both Gem-mediated and CTL-mediated toxicity. Bcl-2 silencing could be exploited therapeutically in tumor vaccine approaches.

[Indexed for MEDLINE]

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